Abstract

The role of brain insulin signaling in the control of food intake in humans has not been thoroughly defined. We hypothesized
that the hormone contributes to the postprandial regulation of appetite for palatable food, and assessed the effects on appetite
and snack intake of postprandial versus fasted intranasal insulin administration to the brain in healthy women. Two groups
of subjects were intranasally administered 160 IU insulin or vehicle after lunch. Two hours later, consumption of cookies
of varying palatability was measured under the pretext of a taste test. In a control study, the effects of intranasal insulin
administered to fasted female subjects were assessed. Compared with placebo, insulin administration in the postprandial but
not in the fasted state decreased appetite as well as intake and rated palatability of chocolate chip cookies (the most palatable
snack offered). In both experiments, intranasal insulin induced a slight decrease in plasma glucose but did not affect serum
insulin concentrations. Data indicate that brain insulin acts as a relevant satiety signal during the postprandial period,
in particular reducing the intake of highly palatable food, and impacts peripheral glucose homeostasis. Postprandial intranasal
insulin administration might be useful in curtailing overconsumption of snacks with accentuated rewarding value.